20mph has become the legal speed limit on most roads in central Brighton and Hove, from this morning.
The city's Green council has introduced the traffic measures for residential and shopping streets in the city, approved by its Transport Committee in January.
It will be legally enforceable, although it is thought unlikely the police will do so. Taxi drivers are also trying to get a judicial review in an effort to stop the go-slow solution.
Road markings and signs have been installed across the the city.
The council says it hopes to reduce the number of crashes and casualties, improve traffic flow and making the city a "safer and better place to live in".
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A damp and cold night ahead. Valentine's Day will start cloudy but become brighter in the afternoon. Risk of showers along the Kent coast.
Cold and damp tonight with outbreaks of rain. A cold and dull start to Valentine's Day but becoming drier and brighter by the afternoon.
Rain turning more patchy this afternoon but more persistent along the coast. Feeling cold in the brisk north-easterly wind.